The membrane properties which control Ca ions uptake and binding by sarcoplasmic reticulum Ca ions -ATPase will be investigated in a reconstituted vesicular system. The effect of different phospholipids on the state of local motion near the enzyme and on overall membrane fluidity will be examined using nuclear magnetic resonance (nmr)spectroscopy and fluorescence polarization. These physical parameters will be correlated with Ca ions uptake and binding. It will then be possible to examine how the enzyme activity and the membrane physical parameters can be influenced by electrostatic effects such as cation concentration and pH which have been implicated in pathological cardiac conditions. Part of this research involves development of a new application of nmr Difference Spectroscopy.